1. Field of the Invention
This invention relates to a method and apparatus for carrying out anti-lock braking in a four wheel drive vehicle, in which a power unit is connected to one of the front and rear axles, the other axle being connected to the power unit via a torque transmission.
2. Description of the Prior Art
In a conventional four wheel drive vehicle, brakes are generally provided on all four wheels thereof.
In this vehicle, the front and rear axles are connected an anti-lock brake system is basically designed to control the braking torque for each wheel or axle individually and thereby retain a slip ratio of each wheel at a suitable level, and it is necessary that the speed of each wheel or axle be varied irrespective of one another. On the other hand, in a vehicle in which the front and rear axles are connected substantially rigidly, these axles interfere with each other insofar that braking action on one affects the other. Therefore, it is impossible to provide suitable anti-lock control for each brake in a conventional vehicle which is provided with a brake on each wheel.
In a vehicle in which the front and rear axles are connected substantially rigidly, setting the wheels on one axle to a suitable slip ratio necessarily cuases the slip ratio of the wheels on the other axle to attain a substantially suitable level.
Therefore, if brakes are provided on the front wheels alone so as to obtain a force for braking all the wheels and these brakes are provided with an anti-lock control means, the above problems can be solved.
However, the braking of all the wheels is effected only by the brakes for the front wheels and therefore the load on the brakes becomes large and it is difficult in some cases to increase the capacity of the brakes due to the small space around the front wheels.